A method for the continuous casting of thin slabs was introduced at the end of the eighties, said method then having become popular in the industry under the name of “compact strip production” (CSP). It was an object at the time to refine conventional continuous casting toward “close-to-final-dimension” casting, that is to say to ultimately cast the slabs so thin such that only the minimum deformation required for reasons of material and forming technology had to be applied in the rolling mill, and that the scope of the rolling stage could thus be reduced.
A plant for casting thin slabs can be derived from WO 2007/101685 A1, for example. After the permanent mold, the cast strand is guided vertically downward by means of a strand guide. When the strand leaves the strand guide, the former is solidified to the core. The cast strand is bent and straightened only upon solidification to the core, so as to avoid any undesired elongation of the strand and any formation of fissures. By virtue of the strand being guided vertically downward and subsequently being diverted to the horizontal, this type of plant is also referred to as a vertical bending plant. A temperature equalization furnace which is not discussed in more detail in the WO publication follows bending and straightening.
FIG. 1a shows a vertical bending plant from the prior art. A funnel-type permanent mold from which the cast steel exits as a strand 1 in a vertically downward manner is identified by the reference sign 10. The strand 1 thus demolded is subsequently guided along a strand guide 20 (continuing in a vertically downward manner) and is cooled by means of cooling segments 30. The cooling segments 30 form the so-called secondary cooling. The strand 1 is completely solidified at or shortly before the end of the last cooling segment 30. The strand 1 subsequently makes its way below the strand guide 20 into the bending region 40 where said strand 1 is exposed to bending forces, on the one hand, and is actively driven in the conveying direction, on the other hand. This is performed by means of rollers and roller pairs 41, the position of which can be derived from FIG. 1a. The straightening region 50 in which the strand 1 is brought to the horizontal alignment adjoins the bending region 40. Rollers 51 are provided here too. One or a plurality of the rollers 41, 51 is/are drive rollers and propel the strand in the transportation direction; other rollers 41, 51 serve for guiding and straightening the strand 1. To this extent, the rollers 41 and 51 form means for driving and bending the strand. The strand 1 by means of a cutting installation 60 (also referred to simply as scissors in some of the figures) is subsequently cut into thin slabs. The singularized slabs are not plotted separately in FIG. 1a. The slabs subsequently run into a furnace 70, the entry of the latter being identified by the reference sign 71. The furnace 70 is embodied as a tunnel furnace and serves as the connection between the casting machine and rolling mill (not illustrated) and for equalizing the thin-slab temperature (when viewed in the cross-sectional direction of the slab). The transportation direction of the strand 1 or of the slabs, respectively, is indicated by an arrow line T.
An exemplary temperature profile of the strand 1 along the transportation direction is shown in FIG. 1b. The graph shows the temperature profile on the surface of the strand 1, in the core, and the average temperature as a function of distance, proceeding from the meniscus on the permanent mold, for a low-carbon material having a slab size of 1600 mm×60 mm at a casting speed of 5.2 m/min. The solidification to the core is approx. 7.4 m, approximately 0.5 m ahead of the last roller of the cooling segments 30. By way of radiation and of contact with the rollers 41, 51, the average temperature of the strand 1 severely decreases between the end of the cooling segments 30 via the bending region 40, the straightening region 50, and the cutting installation 60, up to the furnace entry 71. The average temperature drops from approx. 1247° C. after the cooling segments 30, by approx. 200° C. to approx. 1041° C.
An alternative and more compact construction mode of the CSP plant is shown in FIG. 2a. An exemplary temperature profile of the strand 1 along the transportation direction can be derived from FIG. 2b. In a manner analogous to that of FIG. 1b, the graph of FIG. 2b shows the temperature profile on the surface of the strand 1, in the core, and the average temperature as a function of distance, proceeding from the meniscus on the permanent mold, for a low-carbon material having a slab size of 1350 mm×40 mm at a casting speed of 4 m/min. By contrast to the construction mode of FIG. 1a, only two cooling segments 30 are provided here, and the strand guide 20 is configured so as to be somewhat shorter overall. The plant thus has fewer segments and has a lower overall construction height. The solidification point is shortly before the last roller of the cooling segments 30. Here too, the average temperature drops by approx. 200° C., from 1246° C. to 1041° C.